DEPOSITION OF CESIUM IODIDE PARTICLES IN BENDS AND SECTIONS OF VERTICAL PIPE UNDER SEVERE ACCIDENT CONDITIONS

A relatively small-scale aerosol deposition experiment (called WAVE) in a quartz glass pipe with a 90° bend followed by a short straight section was performed at Japan Atomic Energy Research Institute to investigate the effect of pipe orientation on the cesium iodide (CsI) aerosol deposition. In these basic configurations, the section after the bend was either horizontal, upward and downward, respectively. The upward case showed 5 and 10 times larger CsI mass deposition in the vertical section of pipe than the horizontal and downward configurations, respectively. The experiments were analyzed by coupling a three-dimensional fluid-dynamic and an aerosol behavior codes. The calculations were in reasonable agreement with the measured aerosol mass deposition except for the upward case because the principal CsI deposition mechanism is thermophoresis which depends on the thermal gradient in gas and the gradient was well predicted by the fluid-dynamic code. In order to better predict the deposited mass in vertical section of upward case, Nusselt number which is used for thermophoretic deposition calculation had to be reevaluated carefully by considering the effect of secondary free convection in the vertical pipe which flowed opposite to the main stream.